The present invention relates generally to friction clutches for automotive vehicles and, in particular, to an apparatus for adjusting the hysteresis in a clutch damper.
In conventional passenger cars and trucks, objectional driveline vibrations may occur at certain speeds and road conditions. Some of these disturbances may be eliminated or reduced to an acceptable level with the incorporation of a torsional damper in the driven disc portion of the vehicle clutch. Damping is normally provided by a plurality of circumferentially spaced coil springs operatively connected between relatively rotatable elements of the clutch driven disc assembly.
Clutches with dampers are widely used in all types of power transmission systems. In recent years, particularly in the heavy duty field, conventional spring dampers have not performed satisfactorily when used with the newer higher torque engines. Due to fuel efficiency considerations, these engines operate at a lower speed range with fewer transmission speeds in a critical torsional range and, as a result, impose considerably higher torsional vibration loads on the spring damper than previous engines. This translates into greatly increased stresses on the damper spring which can increase damper spring failure. Additional clutch damage and rapid wear of the associated transmission input shaft and vehicle driveline components may follow.
One solution used to increase the torque capacity of heavy duty clutch driven disc assemblies has been to provide a two part cover designed to house a plurality of circumferentially spaced coaxial pairs of damper springs positioned in aligned openings formed in each cover part. The openings in one cover part engage the ends of both springs while the other cover part engages only the ends of one spring.
The above-described damper assemblies require a clutch assembly in which the outer covers and the hub rotate in unison and the disc and reinforcing plates with the springs rotate in unison relative thereto thus creating a load versus position curve. In some designs, certain additions between these two subassemblies will create hysteresis in the curve. For example, wave washers, Belleville springs or even disc facing material can cause an hysteresis effect.